Top Line: What is temporally feathered radiation therapy (TFRT)?
The Study: We all know what happens when you skip leg day. Think of TFRT as a well balanced recovery schedule for head and neck OARs. TFRT is a radiobiologic and dosimetric concept where organs at risk are alternatively prioritized or deprioritized from day-to-day using multiple treatment plans. Take your standard head and neck treatment plan where total OAR dose is used to control toxicity, and each OAR receives the same fractional dose per day. Now imagine that you have the same composite dose, but one OAR takes a turn getting a larger fractional dose one day of the week while getting much lower dose the other days. The hypothesis is that TFRT may allow for improved tissue recovery on the lighter dose days despite having the same cumulative dose as conventional planning. In this study, 5 patients with p16+ oropharyngeal cancer receiving definitive radiation (+/-) chemo with a prescribed dose of 70 Gy in 35 fractions were planned and 4 were treated using TFRT. At the beginning of TFRT planning, 5 OARs in close proximity to the target were identified. In every patient, the oral cavity, submandibular gland, supraglottis, and pharynx were chosen. The parotid, larynx, and esophagus were also chosen, but not in every patient. Note that serial structures like the spinal cord were not feathered. Five different plans were then made prioritizing 4 OARs at the expense of the 5th. Across plans, the average difference between the high dose fraction and the low dose fraction ranged from 0.15 Gy (per fraction) for the pharynx to 0.34 Gy for the submandibular gland. The primary feasibility goal was plan completion within 15 business days, which was met with a median time from sim to start of 10 days. When it came to treatment delivery, a special daily timeout procedure was done to ensure the correct daily treatment fraction was administered. This study is too small to demonstrate more than the feasibility of the TFRT planning approach, but it introduces an interesting concept for reducing radiation toxicity.
TBL: More data is needed to define optimal differences in high and low fraction dose as well as recovery times for specific tissues, but temporally feathering dose to OARs may be an interesting way to reduce the severity of toxicity from head and neck radiation. | Parsai, Radiother Oncol 2021